[Hyperthermic radiosensitization of a strain of hematopoietic cells from mouse bone marrow, CFU-S]

Employing the technique of the spleen colony-formation the authors investigated the survival curve of the mouse hematopoietic stem cells resulting from increasing doses of X rays (D0 = 0.79 Gy and n = 1.59). The effect of the hyperthermic radiosensitization was measured by comparison with the effects observed in the irradiated CFU-S population previously exposed to hyperthermia. The treatment lasted 60 minutes at 42 degrees C and 12 minutes at 44 degrees C considering the thermal inactivation kinetics in such a way that the survival rate were the same in both cases. The results obtained for D0 = 0.52 Gy and n = 1.0 during 60 minutes at 42 degrees C, and for D00 = 0.61 Gy and n = 1.0 during 12 minutes at 44 degrees C showed that: 1) a synergic effect upon the CFU-S population is produced by the combination of hyperthermia and radiation, 2) for the same survival rate, the radiosensitivity increase produced after the thermic treatment a 42 degrees C and 44 degrees C is of the same order, and 3) such treatments, in both cases, produced a loss of a radioinduced sublethal damage accumulation.